Braun tube



Dec. 27, 1938. SCHLESINGER 2,141,414

BRAUN TUBE Original Filed March 25, 1933 F49. 4. 8 Ja e/#01? M Mai- Patented Dec. 27, 1938 BRAUN TUBE Kurt Schlesinger, Berlin, Germany, assignor to Radioaktiengesellschaft D. S. Loewe, Berlin- Steglitz, Germany Original application March 23, 1933, Serial N...

Divided and this application March 23, 1936, Serial No. 70,423.

In Germany March The light intensity control means heretofore known possess the disadvantage that coupling takes place between intensity control and focussing, i. e., that an increase in the intensity of the ray results simultaneously in an increase in the diameter of the image point. Now, it is particularly important in connection with television processes that the diameter of the image point be maintained constant in the case of all intensities.-

It is accordingly one object of this invention to provide a Braun tube with such intensity controlling means as ensure a. constant diameter of the image point with all image point intensities occurring.

A further object of this invention is to ensure an undisturbed concentration and intensity control of the ray by providing suitable means for centering the control electrode with respect to the cathode, and to avoid disturbances apt to be effected by the leads connected to the system electrodes and by wall charges.

Still further objects and advantages of this invention will be set forth in the following detailed description, by which the invention will be fully understood, especially if it is taken in connection with the appended drawing, wherein Figs. 1 to 4 show several embodiments of the cathode and the control electrode according to the invention, whilst Fig. 5 is a schematic view of a Braun tube having a screening control electrode according to the invention,

Fig. 6 shows a Braun tube including a cathode arrangement according to the invention, and a special electron optical system which preferably shall be employed in combination with said cathode arrangement and Fig. 7 shows a part of a Braun tube provided with a special wall electrode according to the invention.

According to the invention, the control potential is applied between the emissive surface of the hot cathode, which is constructed as an equipotential cathode, and a cylinder surrounding this hot cathode and furnished with a corresponding positive bias. The cathode is furnished with a two-dimensional, say, circular emissive surface. The control element is constructed in the form of a cylinder, terminated by an apertured plate, on which there is furnished a tubelike abutment, which is arranged in such fashion that the apertured plate is situated within the dark space of the cathode, i. e., in the smallest possible spacial disposal to the cathode (for example up to approximately 2 mm.) A spacing of approximately .5 mm. has been found to be particularly suitable. In place of the control cylinder--which exerts a kind ofscreening grid effect-furnished with a tube-like abutment the end aperture thereof may also-be closed ofl by means of a wire netting havlng'a suitable number of meshes, or the cathode may be furnished with a concave emissive surface. The cathode, together with the cylinder having the positive bias and surrounding the same, is preferably arranged exactly centrally within the Wehnelt cylinder. The ray emerging from the Wehnelt cylinder may then .be accelerated and controlled in the manner known per se. There will however be described below some particularly advantageous systems for acceleratingand electron-optically influencing the ray. It is particularlyconvenient to employ a screening anode, which possesses a relatively low potential, and is of such form that spreading effects between the afteracceleration anode and the cathode are safely avoided. The screening anode may also conveniently be furnished with a tube-like abutment. By corresponding selection of the length of this abutment it may be accomplished in simple fashion that the cathode ray emerging from the screening anode essentially always possesses the same rate of movement. The tube is preferably filled with hydrogen or noble gas of suitable pressure.

The arrangement according to the invention acts in the manner of an optical system, in which the tube aperture of the cylinder constitutes a self-luminous surface of varying intensity, which is reproduced in spot-like fashion on the image screen. The electrical field acts approximately on the lines of an optical system, the focus of which may be varied as desired by suitable selection of the potentials. By corresponding selection of the potentials it is possible to reproduce a desired cross-section of the ray or also if necessary the cathode surface itself on the imagescreen in spot-like reduction. It is essential as regards the invention that the direction of the ray, once adjusted, is not varied upon fluctuations in the intensity, i. e., that the spacing between the virtual lens system and the virtual luminous surface remains constant.

In the drawing.v l is the metallic cylinder surrounding the cathode' and having the tubular abutment I, which with the assistance of the bias battery 13 is furnished through the medium of the line l2 with a positive potential, which convenient-1y may amount to approximately 50 volts. The spacing between the end wall of the cylinder and the emlssive surface 8 is made to be as small as possible-approximately 0.5 mm. The tube 1 may be replaced by a grid having a corresponding width of mesh fitted in the opening. Such an arrangement is shown in Fig. 2, wherein 21 is the grid referred to. It is also possible to make the emissive surface of the cathode concave in form. This feature is illustrated in Fig. 3. In this case also the effect according to the invention may be obtained whilst avoiding the tube I. 2 is an insulating ring, in which there is held the insulating tube 3 of the equipotential cathode. 4 is the filament of the cathode, which may be fed by the battery In over the lines 8 and 8 The control current is supplied from the connection point l4, which is shown as a generator, through the medium of the line I I to the equipotential surface of the cathode 5, and accordingly the emissive surface 6. The emissive surface may be in the form of an oxide coating, or also a metalic emissive surface or the like.

As I have found, the production of metallic vapor cathodes in the case of Braun tubes is accompanied by appreciable difliculties insofar as in the case of usual disposal of the metal to be atomized metal is deposited at undesired points. Moreover, metallic vapor cathodes tend to a much greater degree than oxide cathodes towards'emission at the rear and the sides, which results in spreading effects and may cause the tube to be wholly incapable of use.

I Therefore the employing of metallic vapor cathodes in the case of Braun tubes is not pos sible in the arrangement known up to now.

The arrangement according to the invention, however, enables to employ metallic vapor cathodes, as the cathode herein is arranged in a closed protecting casing (screening cylinder i in the figures) which with the exception of an opening provided in the front wall and serving for the outlet of the cathode stream, is, in accordance with the invention, completely closed off, so that no rear or lateral emission of any kind is able to take place, and at the same time a deposit of metallic vapor at undesired points is avoided.

The metal to be atomized in accordance with the invention, may be so arranged that the same, by eddy current heating of the cylinder, may be atomized if necessary with delayed action. Naturally itis also possible to atomize the metal by the passage of current.

As metallic vapor cathode there may be employed, in accordance with the invention, an oxide cathode (alkaline earth metal oxide ortungsten or the like oxide base) with metallic emissive coating applied thereto by atomization. It is also possible to employ wire cores, which consist themselves of a light metal core and possess if necessary an oxide coating. Naturally it is possible in accordance with the invention to employ both directly as well as indirectly heated cathodes. The use of alkaline earth oxide cathodes having metal atomized on to the same has been found to be particularly suitable.

Fig. 4 shows a principal embodiment of the arrangement according to the invention wherein l is the cathode cylinder, which is closed at the rear with the assistance of the insulating plate 2, and which may be provided with side pockets 28 to contain the metal to be atomized, and is closed off at the front by the metal plate having the outlet aperture 1. 5 is the cathode with the current leads 8 and 9.

As shown in Fig. 5, the cathode cylinder may be arranged according to the invention inside of the Wehnelt cylinder. It is also possible to arrange the Wehnelt cylinder before the cathode cylinder. In Fig. 5, I6 is the envelope of the Braun tube. I5 the Wehnelt cylinder, I! the screening anode with the tubular abutment l8, IS the after-acceleration anode, and 20 and 2| are two pairs of control plates. The Wehnelt cylinder, screening anode and after-acceleration anode may be operated with potentials of approximately -150, +250-+500 and +1500-+4000 volts. As the means for supplying the electrodes with the operating potentials are not parts of the Braun tube itself, they are claimed in a separate patent application, viz Ser. No. 662,284, filed March 23, 1933, from which the present one, as relating to the tube structure per se, has been divided out. The screening and control cylinder I, as already set forth, receives a slight positive bias of approximately +30-+60 volts. Taken singly the operating potentials must naturally be adapted to the operating conditions of the single tubes-more particularly dependent on the form and arrangement of the single electrodes. It is readily possible, however, with a once given form and arrangement of the electrodes to adjust the particular optimum potentials.

Naturaly the control means according to the invention may also be employed for any other desired discharge vessel.

In case to employ the Braun tube for oscillograph purposes there is applied a constant potential between the cathode container and the cathode instead of a control potential, which enables in a sufficient manner to completely compensate the space charge effects.

In the arrangement according to the invention the cathode container serves at the same time for screening off against the fields of the high voltage lines, for centering purposes (since in the arrangement according to the inventioncentering is in substance merely a matter of the position of the aperture 1, while the position of the cathode within the cylinder is not critical, centering is naturally considerably facilitated), for closing off towards the outside, which prevents both rear as well as lateral emission and as space charge network.

As pointed out above, one feature of this invention is to avoid disturbances apt to be effected by the leads connected to the system electrodes. More particularly, screening means are, according to the invention, provided, more particularly to screen off those leads connected to a high positive potential.

According to the invention, there is employed as screening means a tube composed of insulating material, which is placed about the lead and may be held by suitable construction of the lead. By the impact of the electrons this tube receives on the surface a negative charge which, as experiments have shown, is sufilciently strong to screen off completely the field effect of the anode. Naturally this screening in accordance with the invention may be made use of, not only at the anode, but also quite generally.

Instead of placing an insulating tube on the lead, an insulating coating, which for example may consist of zirconium oxide or silicate, or if necessary also of a suitable ceramic material, may also be produced on the lead itself to be screened off.

As compared with the known screening means, the screening arrangement according to the invention possesses the advantage of utmost simplicity with completely adequate effect.

Fig. 6 shows the electron optical system which preferably shall be employed in combination with the control arrangement according to the invention. I

In Fig. 6, 25 is the stem of the valve, IS the Wehnelt cylinder (the cathode itself is not visible), I! the screening anode with a small aperture I1. 24 the after-concentration cylinder, I 9 theafter-acceleration anode, 20 and 2| the two pairs of control-plates, which may possess the same potential. It has been proved suitable to arrange the cylinder 24 as close as possible to the screening anode. It is also possible to reach the effect according to the invention in case the cylinder is arranged in about the middle between the .anteand the after-acceleration anode; in contradistinction to this it is unsuitable to ar-' range this cylinder close to the after-acceleration anode. 30, 3!, 33, 36 and 31 are parts of the supporting structure, 39 an isolation separator, for instance consisting of mica. Naturally shape, size and arrangement of the system as well as of the electrodes may be different from those illustrated by way of example in the drawing. The screening anode may be supplied on the side turned towards the after-concentration cylinder with a tube shaped metallic continuation. The supporting wires 30, 3|, 32. 33, 36 and 31 at the same time serve as leads. They are partly surrounded by insulating screens as referred to above (see tubes 40, ll, 42, 43, 46).

It is also possible to give the anode a shape of a little casket. The image screen may suitably be furnished with a thin metallic layer, which nearly possesses the potential of the anode or suitably a higher potential than the after-acceleration anode. Instead of metallizing the image screen itself, on the walls of the tube near the image screen a metallic ring, respectively a metallic deposit possessing the above mentioned potential may be arranged.

The valve may suitably be used with gas-filling in a manner known per se.

The dimensioning of the potentials to be employed depends upon the distance of the image screen from the electron-optical system, as well as upon the shape, the size and the distance of the electrodes between each other. The electrode systemonce fixed, makes it possible without difliculties to so adjust the several voltages that the focus of the electron-optical system lies in the plane of the image screen. As a result of experiments with valves of the usual dimensioning, the required potentials of the electrodes were found to lie within the following limitations; the potential of the space charge controlling cylinder to about 200 volts, screening anode +300- +400 volts; after-concentration cylinder +100- +250 volts; after-acceleration anode +2000- +4000 volts. The total arrangement, in which the Braun tube is operated with such potentials, is claimed in the parent application Ser. No. 662,284, filed March 23, 1933, already mentioned.

Special shaping, size dimensioning or arranging of the electrodes may make it necessary to deviate in not an unessential manner from the above mentioned dimensions of voltages.

In Fig. 7, I6 is the tube body, 29 an auxiliary electrode which is preferably supplied with a potential, which is a little, for instance for 100- 300 volts, lower than that of the after-acceleration anode.

The electrode 29 preferably may consist of a thin metallic layer, i. e., of silver. As is clearly shown in the figure the electrode is arranged near the last deflecting plates pair preferably between the said pair and the luminescent screen. The electrode 29 may have a length of 7-14 cm., if the length of the conical portion of the tube is 26 cm., preferably in this case the electrode may have a length of 11 cm. Generally the electrode must be made as short as to avoid a deflecting effect of said electrode to the cathode ray. The potential, the electrode is to be supplied with, depends on the length of said electrode, and is in each case to be found without difliculty by experiments. If a certain potential shall be employed the length, the electrode must have, is to be found by experiments, by suitable choice of the length of the electrode 29 and of the potential it is supplied with. The electrode 29 makes it possible to produce television pictures which are entirel clear at all points;

I claim:

1. A Braun tube comprising an indirectly heated cathode consisting of an insulating tube, a

heater element arranged inside said tube, an

said cylinder at the side thereof situated next to the closed end of said metallic tube, said plate having a central opening, an anode adapted to have'a high positive potential impressed thereon, a cylindrical abutment connected to said plate at its side facing said anode, said abutment surrounding said plate opening, a fluorescent screen, means to concentrate and means to deflect the cathode ray.

2. A Braun tube comprising an indirectly heated cathode consisting of an insulating tube, a heater element arranged inside said tube, a-n equipotential metallic tube closed at one end surrounding said insulating tube, and a highly emissive substance arranged on the closed end of said metallic tube, a control cylinder adapted to be supplied with a variable control voltage in rela-- tion to said equipotential tube coaxially surrounding said cathode, a plate terminating said cylinder at the side thereof situated next to the closed end of said metallic tube, said plate being disposed at a distance of approximately half a millimetre from the closed end of said metallic tube, said plate having a central opening, means for holding said cathode in said cylinder, said means being secured to said cathode and to said cylinder, an anode adapted to have a high positive potential impressed thereon, a fluorescent screen, means to concentrate and means to deflect the cathode ray.

3. A Braun tube comprising an indirectly heated cathode consisting of an insulating tube, a heater element I arranged inside said tube, an equipotential metallic tube closed at one end surrounding said insulating tube, and a highly emissive substance arranged on the closed end of said metallic tube, a control cylinder adapted to be supplied with a variable control voltage in relation to said equipotential tube coaxially surrounding said cathode, a plate terminating said cylinder at the side thereof situated next to the closed end of said metallic tube, said plate being disposed at a distance of approximately half a millimetre from the closed end of said metallic tube, said plate having a central opening, a network attached to said plate and covering the opening thereof, holding means for holding said cathode within said cylinder, said holding means being secured to said cathode and to said cylinder, an anode adapted to have a high positive potential impressed thereon, a picture receiving screen, means to concentrate and means to deflect the cathode ray.

4. A Braun tube comprising an indirectly heated cathode consisting of an insulating tube, a heater element arranged inside said tube, an equ potential metallic tube closed at one end surrounding said insulating tube, and a highly emissive substance arranged on the closed end of said metallic tube, a control cylinder adapted to be supplied with a variablecontrol voltage in relation to said equipotential tube coaxially surrounding said cathode, a plate terminating said cylinder at the side thereof situated next to the closed end of said metallic tube, said plate being disposed at a distance of approximately half a millimetre from the closed end of said metallic tube, said plate having a central opening, means for holding said cathode within said cylinder, said means being secured to said cathode and to said cylinder, a Wehnelt cylinder surrounding said metallic cylinder, said Wehnelt cylinder being adapted to have a negative bias in relation to said cathode impressed thereon, an anode adapted to have a high positive voltage in relation to said cathode impressed thereon, an anode adapted to means to concentrate and means to deflect the cathode ray.

5. A Braun tube comprising an indirectly heated cathode consisting of an insulating tube, a heater element arranged inside said tube, an equipotential metallic tube closed at one end surrounding said insulating tube, and a highly emissive substance arranged on the closed end of said metallic tube, a control cylinder adapted to be supplied with a variable control voltage in relation to said equipotential tube coaxially surrounding said cathode, a plate terminating said cylinder at the side thereof situated next to the closed end of said metallic tube, said plate being disposed at a distance of approximately half a millimetre from the closed end of said metallic tube, said plate having a central opening, means for holding said cathode within said cylinder, said holding means being secured to said cathode and to said cylinder, a highly emissive vaporizable substance arranged inside said cylinder in connection therewith, an anode, a fluorescent screen, means to concentrate and means to deflect the cathode ray.

6. A Braun tube comprising an indirectly heated cathode consisting of an insulating tube, a heater element arranged inside said tube, an equipotential metallic tube closed at one end surrounding said insulating tube, the closed end of said metallic tube having a concave outer surface, and a highly emissive substance arranged on the closed end of said metallic tube, a control cylinder adapted to be supplied with a variable control voltage in relation to said equipotential tube coaxially surrounding said cathode and being separated from it by the vacuum, a plate terminating said cylinder at the side thereof situated next to the closed end of said metallic tube, said plate having a central opening, an anode adapted to have a high positive potential impressed thereon, a cylindrical abutment connected to said plate at its side facing said anode, said abutment surrounding said plate opening, a fluorescent screen, means to concentrate and means to deflect the cathode ray.

'I. A Braun tube comprising an indirectly heated cathode consisting of an insulating tube, a heater element arranged inside said tube, an equipotential metallic tube closed at one end surrounding said insulating tube, and a highly emissive substance arranged on the closed end of said metallic tube, a control cylinder adapted to have a control voltage in relation to said cathode impressed thereon coaxially surrounding said cathode and being separated from it by the vacuum, a plate terminating said cylinder at the side thereof situated next to the closed end of said metallic tube, said plate having a central opening, a Wehnelt cylinder adapted to have a nega:

tive bias in relation to said cathode impressed thereon surrounding said metallic cylinder, an anode adapted to be maintained positive in relation to said cathode, a second cylinder adapted to have a potential impressed thereon which is lower than that impressed on said anode, a second anode adapted to have a potential impressed thereon which is more positive than that impressed on the first said anode, two pairs of defleeting plates, a fluorescent screen, and an auxiliary electrode arranged between said deflecting plates and said fluorescent screen.

8. A Braun tube comprising an indirectly heated cathode consisting of an insulating tube, a heater element arranged inside said tube, an equipotential metallic tube closed at one end surrounding said insulating tube, and a highly emissive substance arranged on the closed end of said metallic tube, a control cylinder adapted to have a control voltage in relation to said cathode impressed thereon coaxially surrounding said cathode and being separated from it by the vacuum, a plate terminating said cylinder at the side thereof situated next to the closed end of said metallic tube, said plate having a central opening, a Wehnelt cylinder adapted to have a negative bias in relation to said cathode impressed thereon surrounding said metallic cylinder, a highly emissive vaporizable substance arranged inside said cylinder in connection therewith, an anode adapted to be maintained positive in relation to said cathode, a second cylinder adapted to have a potential impressed thereon which is lower than that impressed on said anode, a second anode adapted to have a potential impressed thereon which is more positive than that impressed on the first said anode, two pairs of deflecting plates, a fluorescent screen, and an auxiliary electrode arranged between said deflecting plates and said fluorescent screen.

KURT SCI-ILESINGER. 

